1. Field of the Invention
The present invention relates to a method and a plant for reducing iron ore to pig iron in a blast furnace by means of carbon, wherein a partial quantity of the carbon is admixed to the iron ore in the form of coke which ensures that the bulk material column is loosened and supported and that the gas can penetrate through the bulk material column in the blast furnace, and wherein the remaining partial carbon quantity is injected as a substitute reducing agent into the blast furnace.
2. Description of the Related Art
The injection of carbon carrier, such as, for example, natural gas, heavy oil, fine coal, into the blast furnace as a substitute reducing agent for saving coke has already been practiced for many years.
The simplest and most reliable manner of introducing the substitute reducing agent into the blast furnace is to add it through the blast tuyeres of the blast furnace. In the immediate tuyeres area, the substitute reducing agents are initially combusted with hot air to CO.sub.2 and H.sub.2 O and then reduced to CO and H.sub.2 when impinging upon the coke.
When introducing the substitute reducing agents into the blast furnace, it is desired that a complete combustion or gasification of the substitute reducing agents takes place in the oxidizing tuyeres area of the hearth zone, while simultaneously the blast tuyeres and blast pipes are to be protected as much as possible against destruction due to an early combustion of the substitute reducing agents.
This object is easiest to meet in case of gaseous substitute reducing agents and is most difficult in case of solid substitute reducing agents, such as, for example, fine coal. Therefore, for injecting fine coal as the substitute reducing agent, various coal dust injection systems and blasting methods have been developed over time as described in the publication "Stand der Kohleeinblastechnik in den Hochofen bei den Mitgliedswerken des VDEh" [State of the carbon injection technology in the blast furnaces of member plants of VDEh], Stahl und Eisen 108 (1988), No. 9, pages 459-467. The primary focus and object of the developments was to lower the energy costs and to reduce the coke consumption in the blast furnace by using substitute reducing agents. However, in accordance with experience with actual operations, injection quantities of above 200 kg coal/t pig iron were difficult to achieve permanently for reasons of process technology.